Heretofore, there has been provided a mobile communication system that allows an inter-frequency handover for a mobile station UE in a communication environment including a mixture of multiple cells (frequency cells) using different frequencies.
Specifically, a mobile communication system based on the “LTE (Long Term Evolution)” system specified in the 3GPP employs the following configuration. A mobile station UE measures a radio quality in a cell (inter-frequency cell) neighboring a frequency cell that is currently in communication with the mobile station UE. Then, when determining, with reference to a determination condition, that the measured radio quality satisfies a predetermined radio quality, the mobile station UE transmits a measurement report (Measurement Report) indicating the measurement result to a radio base station eNB. Subsequently, the radio base station eNB determines, in accordance with the received measurement report, that an inter-frequency handover for the mobile station UE should be performed from the frequency cell currently in communication with the mobile station UE to an inter-frequency cell having a better radio quality.
Here, the mobile communication system based on the LTE system not only needs to co-exist with a mobile communication system based on another system that has been already deployed such as a UTRAN (UMTS Terrestrial Radio Access Network) system and a GERAN (GSM EDGE Radio Access Network) system, but also needs to support mobility to and from these mobile communication systems.
Note that, the service to be provided, the transmission rate, the radio efficiency and the like differ among the different mobile communication systems, so that the mobile communication system optimum for the communications differs depending on the terms and conditions or the used service of the user.
In addition, the mobile communication system based on the LTE system supports various bandwidths from 1.4 MHz to 20 MHz. Accordingly, when multiple LTE carriers (frequencies) having different bandwidths exist, the optimum frequency differs depending on the used service.
For example, a broadband carrier (frequency) is preferable in a service where a large amount of data is to be downloaded instantly. However, a broadband carrier (frequency) does not necessarily have to be used in a service such as a voice service or machine-to-machine communications.
In addition, it is preferable to flexibly switch between mobile communication systems (RATs) or between carriers (frequencies) in accordance with the degrees of congestions in the RATs or the frequencies.
Accordingly, there is required a method capable of flexibly switching between the RATs or frequencies in accordance with the terms and conditions or the used service of the user, or the degrees of congestions. In particular, there is required a control method with which a priority level can be designated for each RAT or each frequency.
However, the conventional mobile communication system has a problem that the aforementioned determination condition cannot be flexibly changed between multiple mobile communication systems (RATs) or carriers (frequencies) in accordance with their priorities.
In this respect, the present invention has been made in view of the aforementioned problem, and an object of the invention is to provide a mobile station and a mobile communication method capable of flexibly changing a determination condition for determining whether or not to transmit a measurement report by a mobile station UE.